Generally, a washing machine performs a washing operation using frictional forces generated between laundry and wash water contained in a drum rotated by a drive force from a motor, and the function of a detergent dissolved in the wash water. The drum is a washing tub in which wash water and laundry are contained. The drum is applicable to washing machines of any types, namely, irrespective of a drum type or a pulsator type.
Meanwhile, the driving system of the washing machine uses an indirect power transmission system in which the driving force of the motor is indirectly transmitted to the drum via a belt wound between a motor pulley and a drum pulley, or a direct power transmission system in which the driving force of the motor is directly transmitted to the drum.
The indirect power transmission system, in which the driving force of the motor is indirectly transmitted to the drum via the belt wound between the motor pulley and the drum pulley without being directly transmitted to the drum, has problems of loss of energy and great noise generated during the transmission of driving force. Taking into consideration such problems, use of washing machines using a directly-connected motor has increased.
FIG. 1 is a sectional view illustrating a structure of a conventional drum washing machine.
As shown in FIG. 1, a tub 2 is disposed in a cabinet 1. A drum 3 is centrally disposed in the tub 2 such that the drum 3 is rotatable.
A motor, which includes a rotor 5 and a stator 6, is arranged at the rear of the tub 2. The stator 6 is fixedly mounted to a rear wall of the tub 2. The rotor 5 surrounds the stator 6, and is connected to the drum 3 by a drum shaft 4 extending through the tub 2. Although not shown, magnets are arranged along an inner circumferential surface of the rotor 5 such that opposite polarities are alternately arranged.
A door 7 is mounted to a front side of the cabinet 1. A gasket 8 is arranged between the door 7 and the tub 2. A suspension spring 9a is arranged between the inner surface of the cabinet 1 at the top of the cabinet 1 and the outer surface of the tub 2 at the top of the tub 2, in order to support the tub 2. A friction damper 9b is arranged between the inner surface of the cabinet 1 at the bottom of the cabinet 1 and the outer surface of the tub 2 at the bottom of the tub 2, in order to attenuate vibrations generated at the tub 2 during a spin-drying operation.
A tub support (not shown), which is made of metal, is interposed between the rear wall of the tub 2 and the stator 6, in order to support the weight of the stator 6 and to maintain the concentricity of the stator 6. The tub support has a structure approximately similar to the profile of the rear wall of the tub 2. The tub support is fixed to the rear wall of the tub 2.
When the stator 6 receives electric power, it functions as an electromagnet. In this state, the rotor 5 is rotated by a rotating magnetic field formed between the stator 6 and the magnets of the rotor 5. The rotating force of the rotor 5 is transmitted to the drum via the drum shaft 4.
Recently-developed washing machines have a tendency to provide a large capacity. Due to such a tendency, the motor, which is used to rotate a drum in such a washing machine, must have increased power. For this reason, the sizes of the rotor and stator in the motor must be increased, thereby incurring a problem of a great increase in the size and weight of the motor.
In order to solve this problem, the applicant proposed a washing machine including a dual-rotor type motor, as disclosed in Korean Patent Laid-open Publication No. 2001-0097204 (published on Nov. 8, 2001). In the disclosed dual-rotor type motor, coils are wound on a stator at the inside and outside of the stator, respectively. An inner rotor and an outer rotor are arranged at the inside and outside of the stator, respectively, such that a predetermined gap is defined between each rotor and the stator. By virtue of such a dual rotor structure, the motor can have increased power.
However, such a dual-rotor type motor must be more firmly mounted to a washing machine or the like, correspondingly to the increased-power thereof.